Following a low-carb diet, even for only two days a week, was better than following a calorie-restricted diet every day for losing weight and lowering insulin levels, which are both associated with lower risks of breast and other cancers, says a new study presented Dec. 8 at the American Cancer Research Society meeting in San Antonio.

"Weight loss and reduced insulin levels are required for breast cancer prevention, but are difficult to achieve and maintain with conventional dietary approaches," said Michelle Harvie, a research dietitian at the Genesis Prevention Center, at University Hospital in South Manchester, England.

Harvie, who presented the findings, and her colleagues randomly assigned 115 women, who were all overweight or obese and who also had a family history of breast cancer, to one of three diets.

They were asked to follow either:

•a low-calorie, low-carbohydrate diet for two days a week

•a low-carbohydrate diet that allowed unlimited protein and healthy fats, such as lean meats, olives and nuts, also for two days per week

•a low-calorie, Mediterranean-type diet for seven days a week.

Those in the first group were allowed 650 calories on the two days of their regimen. Those in the first two groups were limited to fewer than 50 grams of carbs on their diet days. The third group was allowed 1,500 calories a day.

The women followed the diets for four months, and 88 completed the study. The highest dropout rate was among the daily, low-calorie group, said Harvie, in which 12, or twice as many women, dropped out compared to the first group, in which six quit. Eight women from the middle group dropped out.

"We know people find it difficult to diet seven days a week, so we tried the two-day approach, which seemed to help women adhere. Many got into the groove and ate better on their off days, too," said Harvie.

Researchers compared the effects of each diet on weight loss, blood markers associated with breast cancer, and insulin levels. Insulin is a cancer-promoting hormone.

The data indicated that both low-carbohydrate diets, even at two days a week, beat the daily calorie-restricted Mediterranean diet for weight loss, body fat reduction and lower insulin levels.

Women on both low-carb plans lost an average of nine pounds, while those on the daily calorie-restricted plan lost five pounds. Insulin levels dropped by 18 percent in the low-carbohydrate groups compared to only 4 percent in the standard low-calorie diet group.

"It is interesting that the diet that only restricts carbohydrates but allows unlimited protein and fats is as effective as the calorie-restricted, low-carbohydrate diet," said Harvie, who plans to further study the effects of carbohydrate intake on breast cancer.